Lactobacillus species, including Lactobacillus crispatus, is the dominant component in vaginal microbiota in one-half of all women with a healthy vagina who produce a substantial amount of lactic acid and hydrogen peroxide to maintain an acidic vaginal environment (pH 3.5–4.5). This inhibits overgrowth of harmful microorganisms such as Group B streptococci, Escherichia coli, Staphyococcus aureus, Gardnerella vaginalis, or other fastidious or uncultivated anaerobes.1 Such anaerobes often result in obstetric, gynecological, or surgical complications.2,3
The study by Amin et al4 in this issue of the Journal of the Chinese Medical Association evaluated the vaginal microbiome from 100 vaginal swabs obtained from 100 women at the reproductive age of 25–50 years. The authors found that nearly 60% of the vaginal samples could identify the presence of Lactobacillus strains, and accidentally detect one pathogen—Clostridium perfringens—an anaerobic Gram-positive bacterium. The authors then used the extracts isolated from the Lactobacillus species to test the in vitro antibacterial activity against C. perfringens. The minimal inhibitory concentration (MIC) for C. perfringens ranged from 15.6 μg/mL to 31.2 μg/mL.4 In addition, the authors further found that the extracts of the Lactobacillus species also showed a significant inhibitory effect on the other pathogens, including Candida albicans (MIC 30–100 μg/mL), S. aureus (MIC 40–100 μg/mL), and E. coli (MIC 25–80 μg/mL).4 The authors concluded that the women without vaginal Lactobacillus strains might be susceptible to nonindigenous and potentially harmful microorganisms.4
This study is interesting and might be of great value, although many questions could be identified in Amin et al's4 investigation. However, there is some chance that the claims of their study could be overstated.
First, the authors did not provide an answer as to whether the women infected with C. perfringens belonged to the Lactobacillus species-rich or the Lactobacillus species-absent environment. Compared with a previous study by the same institute (Health Research Institute, Infectious and Tropical Disease Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran),5 there is no difference in the incidence of presence of the Lactobacillus species between healthy women in Mousavi et al's5 study and healthy unknown women in Dr.'s study4 (66% vs. 59%). In fact, the above finding is not surprising, because the incidence of Lactobacillus species in both studies (59% and 66%) was consistent with a large study (only 58–90% of women with the identified Lactobacillus species).6
Second, the authors failed to provide any evidence showing that women complicated with vaginal infection might have a higher percentage of failure to identify the Lactobacillus species. In fact, Amin et al's4 group did not mention whether this woman who was positive for C. perfringens had identification of Lactobacillus species. In addition, there are many species of Lactobacillus, and previous evidence has shown that different Lactobacillus species can act against other pathogens. One study showed that, compared to the Lactobacillus iners-dominated cervicovaginal microbiota, L. crispatus-dominated cervicovaginal microbiota is less likely to shift to dysbiosis, and is associated with a lower prevalence of sexually transmitted infections.7
Third, the authors did not evaluate the difference in components of the vaginal microbiomes between the presence and absence of Lactobacillus species in women, or show data indicating that women without Lactobacillus species in their vagina will be complicated with more pathogens in their vagina.
Finally, what is the key element for the bactericidal effect? In addition, how did the extract of Lactobacillus species work on C. albicans? The authors failed to mention this, but they provided evidence to show that the antimicrobial activity of extract of Lactobacillus species was unrelated to its acidic nature.4 If true, it is contrary to the conventional wisdom that holds that the acidic environment of the vagina provides a protective role against the overgrowth of opportunistic bacteria.1 That is to say, an acidic environment is only the end product of the presence of Lactobacillus species, and not the main cause of a healthy vagina. If the authors had calculated the pH value of these extracts of Lactobacillus species, and generated the result that the pH of the extract of Lactobacillus species did not correlate with MIC on bacteria, then their conclusion might be more convincing. The authors did show the varying impact of MIC of extract of isolates on the growth of opportunistic bacteria (S. aureus and E. coli); however, if the authors could further identify the main Lactobacillus species in each isolate, such information might be of greater value. We believe that different Lactobacillus species might have different abilities to inhibit these opportunistic bacteria, which requires further research.
In conclusion, two recent publications4,5 of the Journal of the Chinese Medical Association emphasize the importance of the vaginal microbiome in women's health. Further understanding of the interaction of the human body with its “residents” (microorganisms or other living things) could provide a better chance to promote the general health in the larger adult female reproductive-aged population.
Conflicts of interest
The authors declare that they have no conflicts of interest related to the subject matter or materials discussed in this article.
This article was supported by grants from the Ministry of Science and Technology, Taiwan, Executive Yuan (MOST 103-2314-B-010 -043 -MY3), and Taipei Veterans General Hospital (V103C-112; V104C-095; and V105C-096). We appreciate the contributions provided by the Clinical Research Core Laboratory and the Medical Science & Technology Building of Taipei Veterans General Hospital for providing experimental space and facilities.
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